With the advancement of information communication technologies, various wireless communication technologies have recently been developed. Among the wireless communication technologies, a wireless local area network (WLAN) is a technology whereby Internet access is possible in a wireless fashion in homes or businesses or in a region providing a specific service by using a portable terminal such as a personal digital assistant (PDA), a laptop computer, a portable multimedia player (PMP), etc.
The IEEE 802.11n is a technical standard relatively recently introduced to overcome a limited data rate which has been considered as a drawback in the WLAN. The IEEE 802.11n is devised to increase network speed and reliability and to extend an operational distance of a wireless network. More specifically, the IEEE 802.11n supports a high throughput (HT), i.e., a data processing rate of up to above 540 Mbps, and is based on a multiple input and multiple output (MIMO) technique which uses multiple antennas in both a transmitter and a receiver to minimize a transmission error and to optimize a data rate.
The WLAN system supports an active mode and a power save mode as an operation mode of a station (STA). The active mode implies an operation mode in which the STA operates in an awake state capable of transmitting and receiving a frame. On the other hand, the power save mode is supported for power saving of an STA which does not require the active state to receive the frame. An STA supporting the power save mode (PSM) can avoid unnecessary power consumption by operating in a doze mode when it is not a time duration in which the STA can access to its radio medium. That is, the STA operates in the awake state only for a time duration in which a frame can be transmitted to the STA or a time duration in which the STA can transmit the frame.
In the WLAN system, an access point (AP) manages traffic to be transmitted to STAs that operate in the power save mode. When there is buffered traffic to be transmitted to a specific STA, a method is required in which the AP reports this to the STA and transmits a frame. Further, when the STA operates in the doze state, a method is required in which, if there is buffered traffic for the STA, the STA transitions to the awake state to be able to normally receive the frame.